Use Arial font in KOMA Class for section Headings

Question

I would like to use Arial in this document (see below). For some reason the KOMA Class seems to change the section heading font to some other font than Arial. If I change the class to e.g. report it works fine. What is the problem here?

\documentclass[12pt, numbers=noenddot,parskip,headings=small,headsepline,listof=nochaptergap, listof=totoc,index=totoc]{scrreprt}

    \usepackage{fontspec}
    \setmainfont{Arial}

    \begin{document}
    Test Text
    \chapter{Heading}
    Test Test Test
    \section{Header}
    Test Test
    \subsection{Heading}
    Test

    \end{document}

Answer 1

KOMA-Script classes use by the default the font family choosen with \setsansfont for the headings and similar elements.

So you can use either

\setsansfont{Arial}

or

\setkomafont{disposition}{\normalfont\normalcolor\bfseries}

Another possibility is setting the class option sfdefaults=false.

But Arial is a sans serif font. So maybe its better to use

\documentclass[12pt, numbers=noenddot,parskip,headings=small,headsepline,listof=nochaptergap, listof=totoc,index=totoc]{scrreprt}

\usepackage{fontspec}
\setsansfont{Arial}
\renewcommand\familydefault{\sfdefault}

\begin{document}
Test Text
\chapter{Heading}
Test Test Test
\section{Header}
Test Test
\subsection{Heading}
Test
\end{document}